Potted Plant Insects

Q: It is almost that time of year again when we need to move our houseplants indoors. Last year we also moved in annoying small, black gnats. At first, we noticed them in the room with the plants. Over the winter, they moved into the bathroom. Every morning there would be one or two more. We killed them each day, but there were always more. It took until January before we finally stopped seeing them. We don't want to go through this again. What were they, and how do we stop them from coming back in again?

A: Many kinds of flies and other small insects could be the problem, but there are two common ones. First, there is the fungus gnat. The adults are gray or black flies that are small at 1/8 inch long. The larval stage is a 1/4th-inch-long white maggot with a black head. The adults are often found on the soil of potted plants, but they do no harm.

The larvae feed on small roots, and a lot of them can harm a plant. Both the adults and larvae may move spores of soil-borne-disease organisms into plants. They can be controlled by letting the soil dry out a little between waterings. An insecticide that can be poured on the soil will kill the larvae but may need to be applied again in a week to kill any more that hatched from the pupal stage during the week.

The other possibility is the drain fly. They are small 1/4th-inch-long black flies. They are very weak fliers that are often seen on sinks or walls in rooms with a drain of some kind. The larvae feed on the thin, gooey film found in drains, garbage disposals or anywhere there is decomposing organic matter, such as in potted plants.

If they are in soil, sediment or decaying vegetation, then an insecticide will kill them. If they are in a drain line, then cleaning out the drain with your favorite drain cleaner will remove their food source and kill them at the same time.

There are dozens of insects, mites, spiders, slugs, lizards (if you are down South) and other organisms that can come indoors with the houseplants. Don't wait until the weather forecast is for an overnight freeze to begin thinking of bringing in the plants. Bring them in when there is no need for air conditioning or the furnace. This will allow you a couple of weeks to bring them in at your leisure.

Do an inspection of the whole plant, and if necessary, wipe the leaves off with a cotton ball dipped in rubbing alcohol. Inspect the soil and the bottom of the pot for pests hiding underneath or in the plant saucer. If the plant is small enough, pull it out of the pot to see if there are pests among the roots.

Email questions to Jeff Rugg at [email protected] To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.